European airports started to return to life on Tuesday after five days cut off from the rest of the world by a huge ash cloud, but some airspace stayed closed after reports a new plume from Iceland may be on its way.

Italy, Switzerland and France reopened their airports early on Tuesday though many flights remained cancelled, and in Italy only a handful took off in the morning, mainly domestic flights. Hungary, Slovenia and Moldova also resumed flights.

In the UK, flights resumed in Scotland and Northern Ireland, but a ban remained in place over the rest of Britain at least until early Wednesday, aviation authorities said.

Initial plans to resume flights from London later in the day were shelved, but Prime Minister Gordon Brown said airlines were seizing the "window of opportunity" to fly passengers into and out of the country.

Airspace in Finland, Poland and parts of Sweden and Ireland was also closed.

European aviation control agency Eurocontrol said on Tuesday about half of scheduled air traffic in Europe was expected to operate -- about 14,000 flights -- up from a third on Monday.

The European Union, which announced on Monday that its members had reached a deal to reduce the size of the no-fly zone from 0600 GMT on Tuesday, acknowledged progress was slow.

"We know there are still a lot of problems for passengers on the ground," spokeswoman for the executive European Commission Helen Kearns told a briefing. "We are faced with an unprecedented crisis. The disruption will continue over the week."    

Germany said it would maintain its no-fly zone until 1800 GMT, with exceptions. Some airlines were taking advantage of the exceptions to fly. Flag carrier Lufthansa, for example, was flying on sight, which does not require air traffic control approval, to destinations like Seoul, New York and Lagos.

"We are operating about 200 flights today. That is the bulk of our long-haul flights, and domestic and European routes are significantly expanded today," said spokeswoman Claudia Lange.

Monday's EU agreement followed enormous pressure from airlines losing an estimated $250 million a day. "We were quite dissatisfied with the process that brought us here," Iata spokesman Anthony Concil said of the delay before the EU ministers' deal.

"We need to find a better way for decision-making. Nonetheless, yesterday was a step in the right direction."             

The unprecedented disaster has stranded millions of people at the end of the busy Easter holiday season and one analyst estimated it could end up costing global passenger airlines and cargo companies as much as $3 billion.  

Many travellers have spent the past five days desperately trying to get home for school or work by road, rail and sea. - Reuters